Sugarcane response to soil P level and VA mycorrhizae

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1987.Bibliography: leaves 157-167.Photocopy.Microfilm.xiii, 167 leaves, bound ill. 29 cmIn Hawaii, sugarcane (Saccharum spp. hybrid) yields often respond erratically to P fertilization. A field experiment was conducted to determine the external P requirement of sugarcane and to evaluate the contribution of vesicular-arbuscular mycorrhizae to its growth and P nutrition. The variety 62-4671 was grown on a manganiferous Tropeptic Eutrustox, in clots which had been maintained at 10 levels of soil P, as measured by a sorption curve procedure. Half of each plot was fumigated with methyl bromide. Mycorrhizal infection in roots sampled at 8 months averaged 23.5% in the nonfumigated subplots and was 4% or less in the fumigated subplots. At 23 months, mean infection in the fumigated subplots had increased to 27.9%, but this was still significantly lower than the 35.9% mean infection in the nonfumigated subplots. Fumigation caused improved early growth at all soil P levels and depressed plant P concentrations when soil P was 0.200 mg L^-1 in solution or lower. Statistically significant quadratic responses to soil P level were observed for cane and dry matter yields at 23 months. Pol, which represents the amount of sugar in unprocessed juice, decreased linearly with increasing soil P. External P requirements 'Here 0.040, 0.026, and 0.018 mg L^-1 for cane, dry matter, and sugar yields, respectively, indicating that sugarcane yields respond to increasing levels of soil solution P. In comparison to other crop species, sugarcane is only slightly responsive to VA mycorrhizae. Significant Fe-chlorosis occurred in three-month-old ratoon shoots in all fumigated subplots and where soil P exceeded 0.310 mg L- l in the nonfumigated subplots. Leaf Fe declined with increasing soil P and Fe-chlorosis increased as leaf Fe decreased and leaf ~in increased. Plants in the fumigated subplots had elevated tissue Mn concentrations even at the last sampling at 28 months. A greenhouse experiment indicated that a biological factor in the field soil caused early growth depression in sugarcane. In another greenhouse experiment, sugarcane was found to maintain significantly higher plant Mn concentrations than corn (Zea mays L.) or Leucaena (Leucaena leucocephala (Lam) de Wit). Nonmycorrhizal sugarcane had significantly higher plant Mn than mycorrhizal plants. It is 9roposed that sugarcane variety 62-4671 acidifies its rhizosphere and that the presence of mycorrhizae reduces the acidification effect. To determine the effect of P Buffer Power on mycorrhizal dependency, three soils, a Typic Hydrandept, a Tropeptic Eutrustox, and a Tropeptic Eutrustox-sand mixture, were adjusted to